Reproduction apparatus, for example color copiers, are presently on the market which produce copies having portions colored as programmed by the operator. These copiers may work from a monocolor original. U.S. Pat. No. 4,045,218 shows an apparatus in which an original is placed at a work station and an indicator adjusted to identify the lines to be reproduced in a first color. An electrostatic image is formed of the original, and, in response to the indicator, a portion of the image is erased. That electrostatic image is reproduced in a first color. Then, a second electrostatic image is formed, with the complementary portion of the original erased and a second color applied. The two images are then transferred in registry onto a receiver to give a copy of the original but with different colors in the areas designated by the operator.
In actual practice this process has been improved by the introduction of a sonic digitizer to be used by the operator in indicating the portion of the original to be specially treated. Other mechanisms have been suggested for inputting the location of the portions of the image to be specially treated to the control portion of the apparatus. For example, these portions may be highlighted on the original and the highlighting sensed during exposure, to input the control information.
Unfortunately, all of the above apparatus and methods require the creation of at least two separate images in the copy machine. Those two images must then be combined. These two steps in this known method create at least two problems. First, complete copies require two image frames and two exposures and therefore can be made only half as fast with two colors as images can be made with a single color. Second, the images must be combined at a transfer station with proper registration. This is commonly done by either recirculating the copy sheet back to a point at the beginning of the copy sheet path and feeding it through the transfer station again or by securing the copy sheet on a drum which presents the copy sheet to the image frames two times. In the first instance registration is quite difficult and the recirculating path is expensive. In the second instance manufacture of the drum and accurate and complete holding of the copy sheet is quite difficult, requiring vacuum or finger hold downs, either of which adds complexity and expense to the machine and often results in misregistration.
U.S. Pat. No. 4,634,259 is representative of a number of two color systems in which an electrophotosensitive member is charged to a first polarity and exposed to a first color image and then charged to a second and opposite polarity and exposed and toned to a second color image in register with the first exposure. The first toner image may be toned before or after the second charging step. This process, of course, requires two separate registered exposures. The second exposure is made on top of either an electrostatic image or a toner image, either of which images are likely to affect the second exposure.